How do you hold your mouse? Tracking the compatibility effect between hand posture and stimulus size

In keeping with the idea that observing objects activates possible motor responses, several experiments revealed compatibility effects between the hand postures used to report a choice and some characteristics of the stimuli. The real-time dynamics of such compatibility effects are currently unknown. We tracked the time course of a categorization experiment requiring subjects to categorize as natural or artifact figures of big and small objects. Participants reported their choice using either a big mouse (requiring a power grip: a hand posture compatible with the grasping of big objects) or a small mouse (requiring a precision grip: a hand posture compatible with the grasping of small objects). We found a compatibility effect between the grip required by the mouse and the grip elicited by objects, even if it was irrelevant to the task. In a following experiment with the same paradigm, lexical stimuli failed to reproduce the same effect. Nevertheless, a compatibility effect mediated by the target-word category (artificial vs. natural) was observed. We discuss the results in the context of affordance effects literature and grounded theories of cognition.